This contract shall make available the invaluable experience of the Principal Investigator and her co-investigators in the use of the SIV:macaque model for HIV vaccine development. Specifically, this contract shall provide the facilities and expertise to evaluate prospective SIV vaccines in up to 100 rhesus monkeys/year. Monkeys will be immunized, evaluated for both cellular and humoral immune responses to vaccination, and challenged with titered stocks of live virus. Infection which may arise post challenge will be determined by virus re-isolation, polymerase chain reaction amplification of proviral DNA, and serology. All animals will be provided 24 hour veterinary care in a facility accredited by the American for Accreditation of Laboratory Animal Care. Virus stocks to be used for challenge of vaccinates may be prepared and titered in vivo as required. It is hoped that this contract shall provide a systematic analysis of viable vaccine strategies in the nonhuman primate model for AIDS such that implementation of efficacious vaccines in human trials may be expedited.